Image processing device

ABSTRACT

The picture processing apparatus of the present invention has pixel judgment means and pixel correction means. The pixel judgment means comprises target pixel detection means for detecting a target pixel having a peak level out of the input picture signal, and edge detection means for detecting edges, each presenting at a distance of n pixels (n≧1) preceding and succeeding the target pixel. Further, the pixel correction means has correction coefficient selection means wherein a peak level correction coefficient is selected according to an output from the target pixel detection means, and an edge correction coefficient is selected according to an edge detection output. With the picture processing apparatus of the present invention, a level of the target pixel is corrected and an edge of the input picture signal is corrected with the pixels of the input picture signal being corrected according to the peak level correction coefficient and the edge correction coefficient.

TECHNICAL FIELD

[0001] The present invention relates to an image processing apparatusallowing a quality of image of a color cathode-ray tube (color CRT) tobe improved when it is used as a picture monitor. More particularly, itrelates to the one wherein a high horizontal spatial frequency picturepattern having a peak level and a picture pattern having an edge areextracted respectively, and separate corrections are performed on thesepicture patterns, thereby improving sharpness of the picture withoutlosing the color saturation.

BACKGROUND ART

[0002] It is known that, with a picture display apparatus such as thecolor CRT used as a picture monitor, the waveform becomes dull bypassage through signal transmission system of an input picture signalfrom a signal input unit to a cathode electrode of the color CRT.Further, it is not possible to ensure a sufficient bandwidth for a highinput picture signal because of attenuation of a horizontal spatialfrequency bandwidth due to the aperture effect in a color CRT displaysystem.

[0003] It is known that the sharpness of the image is not sufficient forthese reasons. Therefore, for example, when this picture monitor is usedas a computer display or the like, it cannot show a small characterclearly, so that small character information tends to become difficultto see. Further, particularly for thin line display, a white verticalline on a black background tends to be darker, and a black vertical lineon a white background tends to thicken in the horizontal direction.

[0004] For this reason, an attempt has been made to sharpen the pictureby using the following means in the art. First, for the dullness of thewaveform generated in the signal transmission system, correction is madeby using a peaking correction circuit. The peaking correction is aprocessing for compensating the lacking frequency bandwidth byperforming a processing for increasing the gain with respect to a givenspecific horizontal frequency.

[0005] For changing the gain by the horizontal frequency, it isrecommendable that the impedance determining the gain is allowed to havea frequency characteristic. A specific example of the peaking correctioncircuit will be described by reference to FIG. 1. A peaking correctioncircuit 10 is provided between a picture output stage and a cathodeelectrode of the color CRT, and a grounded emitter amplifier is used asthe peaking correction circuit 10, as shown in FIG. 1.

[0006] An input picture signal such as a monochrome picture signal SR ofR is supplied to a base terminal 12 of an NPN transistor Q. A collectorthereof is connected to a power source +Vcc via a resistor 14 and animpedance element 16 which is a serial peaking correction element.Further, an emitter peaking circuit 20 of a resistor 20 a and acapacitor 20 b may be also connected in parallel to an emitter resistor18 thereof.

[0007] Herein, the high frequency gain of the output picture signal isdetermined by the impedance element 16, the resistor 20 a, and thecapacitor 20 b. Therefore, utilizing the peaking correction circuit 10allows the gain for the high frequency component of the input signalfrequency to increase, thereby compensating for the loss due to thesignal transmission system.

[0008] The state of correction by peaking is shown in FIGS. 2A to 2C andFIGS. 3A to 3C. FIGS. 2A to 2C show the case of a white image on a blackbackground, while FIGS. 3A to 3C show the case of a black image on awhite background. FIGS. 2A and 3A show ideal waveforms, and FIGS. 2B and3C respectively show the signal waveforms each deteriorated by passagethrough the signal transmission system. Then, FIGS. 2C and 3Crespectively show the signal waveforms each improved by the peakingprocessing.

[0009] Due to the waveform deterioration in the signal transmissionsystem, for FIG. 2B, white information on a black background darkens,and for FIG. 3B, the line width of black information on a whitebackground increases, as well as the level of the black display portionof the signal increases, resulting in a deterioration in contrast of thedetail (the vertical line of a character, or the like) to be expressed.The reduction in contrast is a serious problem particularly for acomputer display. However, it is indicated that the reduction in leveland the reduction in contrast are both improved by peaking correction asapparent from the waveform processings of FIGS. 2C and 3C.

[0010] On the other hand, for the aperture effect of a CRT displaysystem, correction is performed by enhancing the edge of the inputpicture signal. The edge portion of a picture is enhanced by aperturecorrection whereby preshoot and overshoot are added to the edge portion,so that the apparent performances of the CRT display system are improvedby this enhancement processing.

[0011]FIG. 4 shows a specific example of an aperture correction circuit30. It has a pair of delay circuits 32 and 34 as well as the delaycircuit 32 of the first stage receives an input picture signal from aninput terminal 36. Its delay output is supplied to an adder 50. Then, anadder 46 adds the ones obtained by multiplying the inputs and outputs ofthe respective delay circuits 32 and 34 by coefficients ((−1) fold andtwo fold) as shown by means of coefficient multipliers 40, 42, and 44.The one obtained by multiplying the addition output SRe at a coefficientmultiplier 48 is supplied to the adder 50, which adds it to the outputpicture signal.

[0012]FIGS. 5A to 5E are waveform diagrams each showing the operationswherein picture signals SRa and SRc respectively preceding andsucceeding an input picture signal serving as a reference such as amonochromatic picture signal SRb by one pixel (FIGS. 5A to 5C) areobtained. These are subjected to coefficient multiplication and thenpassed to the adder 46, so that an edge signal SRe as shown in FIG. 5Dis obtained. The coefficient multiplier 48 appropriately adjusts thegain thereof and the one thus adjusted is added to the reference picturesignal SRb, thereby obtaining a picture signal SRo whose leading andtrailing edges are respectively enhanced as shown in FIG. 5E.

[0013] Incidentally, if the peaking correction is performed, it ispossible to improve the above described state in which white informationon a black background darkens, and it is possible to improve the abovedescribed state in which the line width of black information on a whitebackground appears to be large. Further, there are a feature that thedeterioration in contrast is also eliminated, and other features.

[0014] However, if the peaking correction is performed, ringing occurs.Accordingly, particularly for the case as shown in FIG. 3C, the blackinformation looks whitely edged, so that the quality of the image islargely impaired.

[0015] Further, even if ringing roughly has the amplitude characteristicdue to the peaking processing, the group delay characteristic isdifficult to flatten, and ringing increases with an increase in peakingamount.

[0016] Namely, for the peaking correction, the improvement in edgedullness and the inhibition of ringing are not completely compatible.This is because if the peaking amount is decreased, the improvement ofthe dullness of the edge is insufficient, but it is possible to inhibitringing: in contrast, if the peaking amount is increased, it is possibleto improve the dullness of the edge, but ringing becomes noticeable.

[0017] Peaking correction is performed using the resistor, thecapacitor, the impedance element, and the like as described above.However, variations in constants of these elements, and variations invalue due to the temperature characteristics occur, and hence stablepeaking correction is impossible.

[0018] On the other hand, in aperture correction, the following problemsare presented.

[0019] The width of the edge added by aperture correction equals to theunit delay time of the delay circuits 32 and 34 as apparent from FIGS.5A to 5E. Essentially, the edge is added to a picture, and hence it isconstant with respect to the spatial frequency. Namely, it should have aconstant width on a screen.

[0020] However, in the case where the aperture correction processing isapplied to a multi-scan monitor capable of varying the horizontaldeflection frequency, when the horizontal deflection frequency is slow,the edge width on a screen narrows, while when the horizontal deflectionfrequency is rapid, the edge width widens. Too large edge width resultsin an image which appears to be edged, while too small width results inan image insufficiently corrected.

[0021] From these facts, if the aperture correction circuit 30 using thedelay circuits 32 and 34 as shown in FIG. 4 is applied to a multi-scanmonitor or a CRT monitor handling various display resolutions, it is notpossible to obtain a satisfactory image quality.

[0022] For solving this problem, it is recommendable that the circuitconfiguration of FIG. 4 is configured by digital circuits. Further, whenthe delay circuits 32 and 34 are respectively made up of m flip-flopcircuits and the clock thereof is set to be, for example, a pixel clockof the display image, it is possible to change the delay time into mtypes one pixel by one pixel, thereby solving it.

[0023] However, even when the aperture correction circuit 30 isconfigured as such a digital aperture correction circuit, the followingproblem remains.

[0024] The state of aperture correction by a digital method is describedby reference to FIGS. 6A to 6D and FIGS. 7A to 7D. The delay time foraperture correction is defined as being for one pixel (1 dot).

[0025]FIGS. 6A to 6D show the case of a white image on a blackbackground, and FIGS. 7A to 7D show the case of a black image on a whitebackground. FIGS. 6A and 7A show ideal luminance waveforms. FIGS. 6B and7B show the luminance waveforms deteriorated due to the aperture effect,and having lost the sharpness. FIGS. 6C and 7C are respectivelyluminance waveforms after aperture correction. FIGS. 6D and 7D show theluminance distribution waveforms when the picture signals subjected toaperture corrections have been added to a monitor.

[0026] Herein, as shown in FIG. 4, a picture signal is doubled at thecoefficient multiplier 44, and the picture signal is multiplied (−1)fold at the coefficient multipliers 40 and 42. The multiplications bythe coefficients are carried out at all of the edge portions of theinput picture signal. However, essentially, the aperture correctionprocessings are not required to be performed on all the picturecomponents with a high horizontal frequency. In other words, in FIGS. 6Ato 6D or FIGS. 7A to 7D, when a picture pattern Pa showing a thin lineas configured by several pixels (n pixels) and a picture pattern Pbhaving a given width are present, if aperture correction is performed onthe picture pattern Pb, the correction is such that respective edgesbecome sharp. Accordingly, the sharpness is largely improved. Then, thecoefficients of the coefficient multipliers 40 to 44 described above areselected such that the edge component can be extracted and improved insharpness with respect to the picture pattern Pb.

[0027] For this reason, if the aperture correction is performed on thepicture pattern Pa configured by a pattern for n pixels, and having alevel of not less than the peak level, the result is slightly excessivecorrection, or potentially insufficient correction. This is because itis not possible to discriminate between the narrow-width picture patternPa as a thin line having a peak level and the broad-width picturepattern Pb, and to respectively correct them with a conventionalaperture correction circuit.

[0028] Further, with such the conventional aperture correction circuit,the mixing ratio among R, G, and B is changed. This is because such anoperation as to make the mixing ratio among R, G, and B constant is notperformed with the conventional circuit. This improper correction causesa large problem that the color saturation of the image is changed.

[0029] This will be described by reference to FIGS. 8A to 8E and FIGS.9A to 9G. For convenience of description, there will be shown the casewhere a picture signal made up of characters and lines in cyanish color,i.e., in a mixing ratio of R:G:B=0.5:1.0:1.0 on a green background hasbeen inputted.

[0030]FIGS. 8A to 8E show a specific example of the aperture correctioncircuit whereby an edge correction signal is generated from a luminancesignal Y, and this is added to each of the monochrome picture signals(primary color signals) R, G, and B to correct the sharpness thereof.

[0031] In FIG. 8A, the inputs of R, G, and B are set to be Ri, Gi, andBi, respectively. For performing the aperture correction, first, theluminance signal Y is calculated from the following equation:

Y=0.30*Ri+0.59*Gi+0.11*Bi

[0032] An edge signal Yedge of the luminance signal Y is as shown inFIG. 8B. The edge signal Yedge is multiplied by an aperture correctioncoefficient K at the coefficient multiplier 48. Assuming that K=0.5, theresulting signal is added to the monochrome picture signals Ri, Gi, andBi. As a result, corrected monochrome picture signals Ro, Go, and Bo asshown in FIGS. 8C, 8D, and 8E, respectively are obtained.

[0033] Herein, considering the timing for performing the edge correction(time point t0), the ratio of inputted monochrome picture signals is:

Ri:Gi:Bi=0.5:1.0:1.0=1:2:2

[0034] while the ratio of monochrome picture signals after aperturecorrection is:

Ro:Go:Bo=0.76:1.26:1.26=1:1.66:1.66

[0035] This indicates that the mixing ratio of R, G, and B is changed byperforming the aperture correction processing, and the color saturationis changed.

[0036]FIGS. 9A to 9G show a specific example of the case where edgesignals are generated from the monochrome picture signals R, G, and Bthemselves, and these are added to respective monochrome picture signalsR, G, and B, thereby performing the aperture correction. Therefore, inthis case, the aperture correction circuit is required for threechannels of R, G, and B.

[0037] In this case, edge signals Redge, Gedge, and Bedge (FIGS. 9B, 9C,and 9D) are generated from the monochrome picture signals Ri, Gi, and Bi(FIG. 9A), respectively. The edge signals Redge, Gedge, and Bedge aremultiplied by the coefficient K (=0.5) at the coefficient multiplier 48as shown in FIG. 4, and the multiplication outputs are added to theoriginal monochrome picture signals Ri, Gi, and Bi, respectively, at theadder 50. The addition results are shown in FIGS. 9E, 9F, and 9G.

[0038] For example, considering the monochrome picture signal R, theresult is:

Ro=Ri+0.5*Redge

[0039] Also for other monochrome picture signals G and B, calculationcan be performed in the same manner.

[0040] Therefore, considering the same timing (timing point t0) as inFIGS. 8A to 8E, the ratio of R, G, and B at this time is:

Ro:Go:Bo=1.0:1.0:2.0

[0041] This indicates likewise that the mixing ratio of R, G, and B ischanged, and the color saturation is changed between input and output.

[0042] Therefore, when this aperture correction processing is applied toa computer display, it becomes impossible to reproduce the hue withfidelity. This indicates that the processing is not suitable for theapplication requiring high resolution and high fidelity.

DISCLOSURE OF THE INVENTION

[0043] This invention proposes an image processing apparatus capable ofimproving the sharpness without deteriorating the color reproducibility.

[0044] The image processing apparatus of this invention comprises pixeljudgment means and pixel correction means each receiving digital inputpicture signal of R, G, and B, respectively, wherein the pixel judgmentmeans includes target pixel detection means for detecting a target pixelhaving a peak level out of the input picture signal, and edge detectionmeans for detecting an edge from a total of 2n+1 pixels of the targetpixel and n pixels preceding and succeeding the target pixel, whereinthe pixel correction means includes a correction coefficient selectionmeans for selecting a peak level correction coefficient according to anoutput from the target pixel detection means, and for selecting an edgecorrection coefficient according to an output from the edge detectionmeans, and wherein a level of the target pixel is corrected and an edgeof the input picture signal is corrected with a pixel of the inputpicture signal being corrected according to the peak level correctioncoefficient and the edge correction coefficient, respectively.

[0045] In this invention, this image processing apparatus is configuredso as to perform the function of aperture correction. It has a means fordetecting a picture pattern identified by the signal levels of a totalof (2n+1) pixels of the target pixel and at least n pixels (n is notless than 1. In the embodiments, it is assumed that n=1) preceding andsucceeding the target pixel, or the signal level difference among thesepixels for each of the RGB digital picture signals (monochrome picturesignals).

[0046] Then, when a picture pattern to be corrected is detected for anyone of R, G, and B, the correction determined based on the resultobtained by performing such a logical or numerical processing that thedetection result is reflected in a single or a plurality of outputresults is added to respective picture signals of R, G, and B to correctthe picture pattern.

[0047] A narrow-width picture pattern such as a thin line pattern and abroad-width picture pattern are discriminated between each other, andrespectively corrected in this manner. In consequence, it is possible toeliminate the excess or deficiency of the correction amount particularlywith respect to the narrow-width picture pattern. Further, performingsuch an arithmetic processing of the correction amount that the ratio ofR, G, and B becomes constant allows the edge correction to performwithout changing the mixing ratio of R, G, and B. As a result, it ispossible to improve the sharpness of the picture pattern. Since theimage processing apparatus in accordance with this invention is based ondigital processing, it is capable of performing a stable signalprocessing without being affected by variations in circuit elements.

[0048] As described above, according to this invention, it is soconfigured that the sharpness is improved by performing the respectiveindividual correction processings on specific picture patterns.

[0049] This can improve the deterioration in sharpness when an imagehaving a high horizontal spatial frequency is displayed without causingchanges in edging and color saturation, thereby allowing small characterinformation and the like to sharply show.

[0050] Further, in accordance with this invention, by appropriatelyselecting the correction coefficient and the like, it is possible toperform the optimum correction according to the signal characteristicssuch as frequency and resolution of the input signal, or theperformances of each CRT monitor determined by the aperturecharacteristics of CRT, i.e., the relationship between the beam spotsize and the display signal frequency, the frequency characteristics ofa picture amplification circuit and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

[0051]FIG. 1 is a connection diagram of a peaking correction circuit;

[0052]FIGS. 2A to 2C are waveform diagrams used for the operationaldescription;

[0053]FIGS. 3A to 3C are waveform diagrams used for the operationaldescription;

[0054]FIG. 4 is a connection diagram of an aperture correction circuit;

[0055]FIGS. 5A to 5E are waveform diagrams used for the basicoperational description;

[0056]FIGS. 6A to 6D are waveform diagrams used for the description ofthe aperture correction operation;

[0057]FIGS. 7A to 7D are waveform diagrams used for the description ofthe aperture correction operation;

[0058]FIGS. 8A to 8E are waveform diagrams used for the description ofthe aperture correction operation;

[0059]FIGS. 9A to 9G are waveform diagrams used for the description ofthe aperture correction operation;

[0060]FIG. 10 is a system diagram of the essential parts showing anembodiment of an image processing apparatus in accordance with thisinvention;

[0061]FIG. 11 is a diagram showing the relationship among the inputsignal frequency, the division ratio, and the correction coefficient;

[0062]FIG. 12 is a system diagram of the essential parts showing anembodiment of a judgment circuit;

[0063]FIGS. 13A to 13J are waveform diagrams used for the operationaldescription;

[0064]FIG. 14 is a system diagram of the essential parts showing anembodiment of a monochrome judgment circuit;

[0065]FIGS. 15A to 15K are waveform diagrams used for the operationaldescription;

[0066]FIG. 16 is a waveform diagram of the essential parts showing anembodiment of a correction circuit;

[0067]FIG. 17 is a waveform diagram showing the input and outputcharacteristics of an A/D converter;

[0068]FIGS. 18A to 18I are waveform diagrams used for the description ofthe operation by peaking correction;

[0069]FIGS. 19A to 19I are waveform diagrams used for the description ofthe operation by peaking correction;

[0070]FIGS. 20A to 20I are waveform diagrams used for the description ofthe operation by aperture correction;

[0071]FIG. 21 is a system diagram of the essential parts showing anotherembodiment of the monochrome judgment circuit;

[0072]FIG. 22 is a waveform diagram used for the operationaldescription; and

[0073]FIG. 23 is a system diagram of the essential parts showing anotherembodiment of the image processing apparatus in accordance with thisinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0074] A description will be given to the case where an embodiment of animage processing apparatus in accordance with this invention is appliedto a picture display apparatus using a color CRT as a monitor byreference to FIG. 10.

[0075] In the embodiment shown in FIG. 10, an image processing apparatus100 in accordance with this invention is connected to a previous stageof a picture amplifier 10 connected to the cathode side of a color CRT1.

[0076] The image processing apparatus 100 is a substitute for aconventional aperture correction circuit. In this invention, it detectsa picture pattern (pixel pattern) identified by the signal levels of thetarget pixel and at least respective one pixels preceding and succeedingthe target pixel, or the signal level difference among these pixels.When a picture pattern to be corrected is detected for any one of R, G,and B, the correction determined based on the results obtained byperforming such logical or numerical processing that the detectionresult is reflected in a single or a plurality of output results isadded to respective R, G, and B picture signals. Thus, the peak and theedge pattern are corrected out of the picture pattern.

[0077] To that end, first, after converting an input picture signal intodigital form, what picture pattern the picture signal has become isdetermined on a monochrome basis for each color of R, G, and B. Then,according to the results obtained by performing the logical or numericalprocessing of 3 results, further according to the pixel clock frequencydetermined from the vertical synchronizing signal and the horizontalsynchronizing signal of the input signal, such a correction amount as togive an optimum result is determined.

[0078] When each color of R, G, and B is judged, the results obtained bycomparing a total of (2n+1) pixels of the target pixel and n pixelspreceding and succeeding the target pixel (n is an integer) in heightwith M, for example, two judgment levels are logically or numericallyprocessed. As a result, finally, the correction amount is uniquelydetermined for every pixel. By multiplying this correction amount torespective picture signals of R, G, and B, it is possible to perform thecorrection while keeping constant the ratio of R, G, and B signal levelsof the input.

[0079] Therefore, this image processing apparatus 100 comprises ajudgment circuit 66 functioning as a pixel judgment means, and acorrection circuit 68 functioning as a pixel correction means.

[0080] Monochrome picture signals (analog signals) SR, SG, and SB forrespective R, G, and B are supplied to an A/D converter 64 via aterminal 62, and converted to digital signals. The digitized monochromepicture signals SR, SG, and SB are individually supplied to the judgmentcircuit 66 and the correction circuit 68. At the judgment circuit 66,out of the input monochrome picture signals SR, SG, and SB, specificpicture patterns are respectively judged. When such a specific picturepattern is present, the correction circuit 68 performs the levelcorrection processing on the picture pattern to carry out theimprovement processing of the sharpness.

[0081] The monochrome picture signals SR′, SG′, and SB′ having improvedsharpness are converted back to analog signals at a D/A converter 70.The analog monochrome picture signals SR′, SG′, and SB′ are subjected topeaking processing at the picture amplifier 10, and then supplied to thecolor CRT 1.

[0082] The color CRT 1 is available for a multi-scanning use. Therefore,a horizontal synchronizing signal HS subjected to synchronizingseparation from the input picture signal is supplied to both of afrequency measurement circuit 76 and a PLL circuit 78 via a terminal 72.Further, a vertical synchronizing signal VS subjected to synchronizingseparation from the input picture signal is supplied to the frequencymeasurement circuit 76 via a terminal 74.

[0083] For the multi-scanning-capable picture display apparatus, aplurality of combinations of the horizontal frequency and the verticalfrequency are present as shown in FIG. 11. Therefore, which pattern offrequencies make up the input picture signal is required to bedetermined. Accordingly, the frequency measurement circuit 76 judges thecombination of frequencies.

[0084] The measured horizontal and vertical frequency values aresupplied to a control unit 80 configured by a microcomputer. Then, byreference to a memory means 82 (such as a ROM) in which the informationas in FIG. 11 is stored, a division ratio determined by the measuredfrequencies is supplied to the PLL circuit 78. For example, when thehorizontal frequency is 91.1 kHz, and the vertical frequency is 85 Hz, adivision ratio “1728” is selected. The PLL circuit 78 is driven by thisdivision ratio, and a clock CK configured with a frequency appropriateto this division ratio is generated. By this clock CK, the monochromepicture signals SR, SG, and SB are subjected to digital conversion, andconverted back to analog signals.

[0085] From the control unit 80, m reference levels are prepared forpicture pattern judgment with respect to the judgment circuit 66. Inthis embodiment, reference levels HL and LL of two high and low valuesare supplied. The memory means 82 also stores correction coefficientsPC, RC, and FC (the detail will be described later), as shown in FIG.11, for improving the sharpness on the picture pattern other than thedivision ratio for the PLL circuit 78. The correction coefficient PC isa peak level correction coefficient corresponding to the picture patternPa of which the peak level is made up of n consecutive pixels. Forconvenience of description, the case where n=1 will be illustrated.

[0086] Whereas, the correction coefficients RC and FC are edgecorrection coefficients each corresponding to the picture pattern Pb ofwhich the peak level is made up of not less than (n+1) consecutivepixels. These correction coefficients PC, RC, and FC are stored in thememory means 82 such as a ROM together with the division ratio and thelike, and supplied to the judgment circuit 66 and the correction circuit68 via the control unit 80.

[0087] The configuration of each unit in the image processing apparatus100 thus configured will be described by reference to FIG. 12 andsubsequent figures.

[0088] The judgment circuit 66 judges the peak and the edge pattern byusing a total of (2n+1) pixels of the target pixel and n pixelspreceding and succeeding the target pixel. Therefore, out of the inputpicture signal, the picture pattern Pa made up of the target pixelhaving a peak level, in other words, the pattern Pa wherein the peaklevel is made up of n consecutive pixels is detected. In addition, bothedges of the picture pattern Pb wherein the peak level is made up of notless than (n+1) pixels are detected.

[0089] The judgment circuit 66 judges the specific picture patterndescribed above for each color of R, G, and B using monochrome judgmentcircuits 90R, 90G, and 90B as shown in the embodiment in FIG. 12. Tothat end, to the monochrome judgment circuit 90R, a monochrome picturesignal SR of R is supplied from a terminal 92 r. Hereinafter, in thesame manner as above, to the monochrome judgment circuit 90G, amonochrome picture signal SG of G is supplied from a terminal 92 g, andto the monochrome judgment circuit 90B, a monochrome picture signal SBof B is supplied from a terminal 92 b.

[0090] Further, to these monochrome judgment circuits 90R to 90B, ahigh-level reference level HL is supplied in common from a terminal 94h, and a low-level reference level LL is supplied in common from aterminal 94 l for level judgment of the picture pattern.

[0091] These reference levels HL and LL are both used for eliminatingthe picture signal having an ordinary level, and detecting only thespecific picture patterns Pa and Pb each having a large level. In thisembodiment, the reference level HL is set to be the level close toroughly 90% of the white level. Whereas, the other reference level LL isset to be the level of roughly 10% up of the black level.

[0092] Subsequently, a judgment example at the monochrome judgmentcircuit 90R when it is set that n=1 is shown in FIGS. 13A to 13E. FIG.13A is an example of picture patterns Pa and Pb. At the time of thepicture pattern Pa for a pixel, which is a narrow-width peak pattern,the monochrome judgment circuit 90R delivers the same peak detectionpulse PDR as the pattern (FIG. 13B). At the time of the picture patternPb, which is broader than this and is made up of not less than twopixels, it delivers a detection pulse RDR corresponding to the leadingedge portion, and a detection pulse FDR corresponding the trailing edgeportion (FIGS. 13C and 13D).

[0093] At the time of a picture pattern of FIG. 13F in white/blackinverted relation to FIG. 13A, the pattern can also be considered to bemade up of a picture pattern Pc made up of a black level for one pixel,and a picture pattern Pd of a black level made up of not less than onepixels. Alternatively, it can be considered to be the picture pattern inwhich all of not less than one pixels preceding and succeeding thepicture pattern Pb is black level.

[0094] Therefore, the peak detection pulse PDR cannot be obtained (FIG.13G). However, since the picture pattern Pb is present, in this case,the edge detection pulses RDR and FDR are obtained at their respectiveedge portions (FIGS. 13H and 13I). Thus, the detection pulses PDR, RDR,and FDR responding for the specific picture patterns Pa and Pb arerespectively obtained.

[0095] Respective monochrome judgment circuits 90G and 90B of G and Balso judge their respective picture patterns Pa and Pb. When thecorresponding picture patterns are present, the detection pulses (PDG,RDG, and FDG) and (PDB, RDB, and FDB) are obtained from the monochromejudgment circuits 90G and 90B, respectively.

[0096] From the foregoing description, each of the monochrome judgmentcircuits 90R, 90G, and 90B has a level judgment function of judging thelevel of the target pixel and the pixels preceding and succeeding thetarget pixel, and an edge judgment function of judging the leading andtrailing edges of the target pixel.

[0097] Out of the detection pulses judged in the foregoing manner, thedetection pulses corresponding to the same picture pattern arerespectively supplied to their respective corresponding common ORcircuits 96P, 96R, and P96F, and ORed. Therefore, when the objectivepicture pattern Pa or Pb is present in any of respective monochromepicture signals SR, SG, and SB, the corresponding OR outputs PDO, RDO,and FDO are obtained. These OR outputs PDO, RDO, and FDO are supplied tothe correction circuit 68.

[0098] Since the monochrome judgment circuits 90R to 90B are the same inconfiguration, for example, only the monochrome judgment circuit 90R ofR will be described, and a description on other configurations and theoperations are omitted.

[0099]FIG. 14 shows an embodiment of the monochrome judgment circuit 90Rof R. A description will be given by reference to FIGS. 15A to 15K.

[0100] The monochrome judgment circuit 90R comprises a pair of cascadeddelay circuits 110 and 112. Both of these are made up of flip-flopcircuits. To the delay circuit 110 of the first stage, the monochromepicture signal SR (SRa) of R is supplied. Therefore, upon input of themonochrome picture signal SRa as shown in FIG. 15A, monochrome picturesignals SRb and SRc shifted by one pixel respectively shown in FIGS. 15Band 15C are obtained from the delay circuits 110 and 112, respectively.

[0101] For convenience of description, if it is assumed that themonochrome picture signal SRb obtained as the output from the delaycircuit 110 of the first stage is a target pixel, the input thereof isthe succeeding pixel, and the monochrome picture signal SRc obtained asthe output from the delay circuit 112 of the subsequent stage is thepreceding pixel.

[0102] The monochrome picture signals SRa, SRb, and SRc are supplied tocomparators 114, 116, and 118, respectively, and compared in level withthe high-level reference level HL (see FIG. 15A). By the levelcomparison, comparison outputs SRHa, SRHb, and SRHc shown in FIGS. 15D,15F, and 15G, respectively are obtained therefrom.

[0103] Further, the monochrome picture signals SRa and SRc are suppliedto comparators 120 and 122, respectively, and compared with thelow-level reference level LL (see FIG. 15A). Comparison outputs SRLa andSRLc shown in FIGS. 15E and 15H, respectively are obtained therefrom.

[0104] These comparison outputs are supplied to their respectivecorresponding AND circuits 124, 126, and 128. The first AND circuit 124is used for detecting the picture pattern Pa. To this, the comparisonoutput SRHb from the comparator 116, and the comparison outputs SRLa andSRLc respectively from the comparators 120 and 122 are supplied. Whenall of the levels of the pixels preceding and succeeding the targetpixel are high level (FIGS. 15D, 15E, and 15H), it judges the targetpixel as being the specific picture pattern Pa, and delivers a detectionpulse (AND output) PDR (FIG. 15I).

[0105] Incidentally, even if the picture pattern Pb of consecutive highlevels for several pixels is inputted with respect to the picturepattern Pa having a peak level for one pixel, this is not identified asthe picture pattern Pa for one pixel for the following reason. In thiscase, the respective comparison outputs SRHb and SRLa from thecomparators 116 and 122 become high level, but the comparison outputSRLa from the comparator 120 becomes low level. Therefore, by ANDingsuch outputs, it is possible to discriminate the picture pattern Pahaving a peak level for one pixel with reliability.

[0106] The second AND circuit 126 is a logical circuit for detecting theleading edge portion. In this case, other than the comparison outputSRHb from the comparator 116, the respective comparison outputs SRHa andSRLc from the comparators 114 and 122 are supplied to the second ANDcircuit 126, and ANDed. At this step, the detection pulse RDR as shownin FIG. 15J is obtained in association with the picture pattern Pb.

[0107] Also in this second AND circuit 126, only for the high-levelpicture pattern Pb of a plurality of consecutive pixels, the detectionpulse RDR corresponding to the leading edge portion is obtained and noresponse occurs to the picture pattern Pa for one pixel. This isbecause, at the timing to of detecting the picture pattern Pa (timing atwhich the target pixel is positioned), the comparison outputs SRHb andSRLc are high level, while the comparison output SRHa is low level.

[0108] The third AND circuit 128 provides the detection pulse FDRcorresponding to the trailing edge portion out of the picture patternPb. To that end, other than the respective comparison outputs SRHb andSRHc from the comparators 116 and 118, the comparison output SRLa fromthe comparator 120 is supplied to the AND circuit 128. As a result, onlyfor the trailing edge portion of the picture pattern Pb, the comparisonoutputs SRLa, SRHb, and SRHc from the three units become high level, andat this timing, the detection pulse FDR is obtained (see FIG. 15K). Alsofrom the third AND circuit 128, an AND output is obtained only for thepicture pattern Pb, and no AND output is obtained for other picturepatterns.

[0109] With such a configuration, the detection pulses PDR, RDR, and FDRcorresponding to their respective specific picture patterns of themonochrome picture signal SR of R are obtained. Also in the monochromejudgment circuits 90G and 90B with respect to other monochrome picturesignals, the same processings are performed to detect the specificpicture patterns Pa and Pb contained in their respective picturesignals. Their respective detection pulses are merged at the OR circuits96R, 96G, and 96B shown in FIG. 12, resulting in selection pulses PDO,RDO, and FDO, respectively.

[0110] Subsequently, an embodiment of the correction circuit 68 will bedescribed by reference to FIG. 16. The correction circuit 68 comprises aselector 102 for selecting the correction coefficients PC, RC, and FCcorresponding to a picture pattern, and multipliers 104R, 104G, and 104Bfor multiplying the selected correction coefficient and the inputmonochrome picture signal.

[0111] To the selector 102, the correction coefficient PC, RC, or FCcorresponding to the picture pattern is supplied from the control unit80 by reference to the memory means 82. As shown in FIG. 11, for theportion corresponding to the picture pattern Pa, the correctioncoefficient PC is used as the correction coefficient for the peak level.As the respective correction coefficients at the leading and trailingedge portions in the picture pattern Pb, the correction coefficients RCand FC are used. In this embodiment, the respective correctioncoefficients RC and FC used for the edge portions are the same value.Both of the correction coefficients are not less than 1.0, and the valueof PC is a larger value than RC and FC.

[0112] In the selector 102, the selection pulses PDO, RDO, and FDO areused for selecting the correction coefficients PC, RC, and FC,respectively. In other words, since the selection pulse PDO correspondsto the picture pattern Pa, the correction coefficient PC is selectedwhen the selection pulse PDO has been obtained (see FIGS. 13E and 13J).For the same reason, when the selection pulse RDO has been obtained, thecorrection coefficient RC for the leading edge portion is selected. Whenthe selection pulse FDO has been obtained, the correction coefficient FCfor the trailing edge portion is selected. No correction is made on thepicture area other than the peak level and the edge, and hence thecorrection coefficient at that time is 1.0.

[0113] The selected correction coefficient is supplied in common to themultipliers 104R, 104G, and 104B, and multiplied to the monochromepicture signals SR, SG, and SB, respectively. As a result, themonochrome picture signals SR′, SG′, and SB′ corrected in level andimproved in dullness of waveform are outputted.

[0114] The monochrome picture signals SR′, SG′, and SB′ are convertedback to analog signals at the D/A converter 70 shown in FIG. 10. Herein,the output from the correction circuit 68 is increased by the correctionamount (by the amount resulting from multiplication by the correctioncoefficient) as compared with the input. Therefore, for performinganalog conversion without degrading the resolution in the direction ofamplitude of the signal subjected to digital conversion, the dynamicrange is required to be enlarged by the correction amount.

[0115] Therefore, in this embodiment, as shown in FIG. 17, the input andoutput characteristics of the D/A converter 70 are enlarged. Forexample, if it is assumed that the output is enlarged up to 150% bymultiplication processing when the D/A converter 70 has an 8-bit outputand an output amplitude of 0.7 Vpp, the dynamic range may be 50%enlarged so that an output amplitude of 1.05 Vpp for an input value of383 is obtained relative to an output amplitude of 0.7 Vpp for an inputvalue of 255 as shown in the diagram.

[0116] The D/A converter 70 is generally so configured that the outputamplitude can be determined based on the externally applied referencevoltage and the external resistance. Therefore, it is recommendable thata not less than 9-bit D/A converter is prepared, and adjusted so as toobtain the input and output characteristics as shown in FIG. 17. It isalso possible to perform compression processing so as to make themultiplication output fall within a range up to a maximum value of 255,not enlarging the dynamic range.

[0117] Subsequently, the waveform improvement and the color saturationin a picture display apparatus when the image processing apparatus 100in accordance with this invention thus configured is used will beanalyzed.

[0118] First, even if the peaking correction is performed by using themonochrome picture signals SR′, SG′, and SB′ obtained by the use of theimage processing apparatus 100 shown in FIG. 10, the ringing as in theart is not generated. In other words, it is possible to correct thedullness of the picture waveform while inhibiting the ringing.

[0119] As for a picture signal having white information on a blackbackground, a description will be given by reference to FIGS. 18A to18I. In FIGS. 18A to 18I, for facilitating the description, it isassumed that all of R, G, and B have the same waveform, and it isassumed that the monochrome picture signal of R is shown in the figure.Then, it is assumed that according to a result of horizontal andvertical frequency measurements, as the correction coefficients,

[0120] PC=1.5

[0121] RC=1.25

[0122] FC=1.25

[0123] have been selected as shown in FIG. 11.

[0124] Incidentally, with the correction coefficients PC, RC, and FCshown in FIG. 11, the higher the horizontal and vertical frequencies ofthe input signal is, the larger values the correction coefficient valuesare. This is because the peak level of a beam spot is reduced due to theaperture effect of the signal transmission system and a monitor 1 withan increase in input frequency. For compensating the reduction in peaklevel, the correction coefficient values increases with an increase ininput frequency.

[0125] Further, FIGS. 18A and 18B show input signal waveforms obtainedby A/D converting a signal waveform deteriorated in the signaltransmission system, and a signal not undergoing waveform deterioration,respectively. Further, the beam response luminance distribution when thesignal waveform of FIG. 18A has been added has a more dull form shown inFIG. 18A′ than the one shown in FIG. 18A. From the signal waveform ofFIG. 18B, the detection pulses PDR, RDR, and FDR shown in FIGS. 18C,18D, and 18E, respectively, are obtained at the judgment circuit 66.Then, by the selection pulse comp (PDO, RDO, and FDO) ORed according tothese detection pulses PDR, RDR, and FDR, the foregoing correctioncoefficients are selected, and the result is as shown in FIG. 18F.

[0126] At the picture pattern Pa, the correction coefficient (PC=1.5) isselected. At the picture pattern Pb, the correction coefficients(RC=FC=1.25) at respective edge portions are selected. Since nocorrection is made on other picture areas, each of the correctioncoefficients at the picture areas is 1.0.

[0127] As a result, at the picture pattern Pa, as shown in FIG. 18G,since PC=1.5, the level is corrected to:

(255*1.5)=383

[0128] At the leading and trailing edge portions of the picture patternPb, respectively, RC=FC=1.25, so that the level is corrected to:

(255*1.25)=319

[0129] Upon D/A converting the corrected digital picture signal, as wellas passing it through the signal transmission system, the deteriorationof the signal occurs, resulting in the signal waveform as shown in FIG.18H. At the picture pattern Pa out of this, a signal waveform slightlydeteriorated than the value of FIG. 18G occurs, but the level is notless than 1.0, resulting in an appropriate value as shown FIG. 18I interms of the peak response luminance distribution. This is due to thewaveform deterioration resulting from the aperture effect. However, ifthe foregoing correction coefficients are employed in consideration ofthe aperture effect, it is also possible to effectively suppress theovershoot amount in the picture pattern Pb. In consequence, the levelbecomes minimal, and becomes almost inconspicuous.

[0130] As for a picture signal having black information on a whitebackground, the result is as shown in FIGS. 19A to 19I. As apparent fromthe waveform diagrams of FIGS. 19H and 19I, it is possible to improvethe line width of the picture pattern Pa than in the art. The otherprocessings are the same as with FIGS. 18A to 18I, and hence thedescription thereon is omitted.

[0131] Then, a consideration will be given to the effect on the colorsaturation when correction processing has been performed by the imageprocessing apparatus 100 in accordance with this invention.

[0132] A description will be given based on a signal in which cyanishcharacters and lines are present on a green background as illustrated inFIGS. 9A to 9G as an input picture signal. As for the reference levelsHL and LL to be used for level judgment of the input picture signal, ithas been assumed that HL=0.9 and LL=0.1 similarly as described above.Further, the level relationship for a picture signal such as a cyaniccharacter on a green background is assumed to be, as shown in FIG. 20A:

[0133] Gi=1.0

[0134] Ri=0.5

[0135] Bi=1.0

[0136] As a result, from the respective monochrome judgment circuits 90Rand 90G of R and G, the detection pulses (PDR, RDR, and FDR) and (PDG,RDG, and FDG) are not obtained as with FIGS. 20B and 20C.

[0137] In contrast, from the monochrome judgment circuit 90B of B, thedetection pulses (PDB, RDB, and FDB) as shown in FIG. 20D are obtained.Therefore, the same selection pulses PDO, RDO, and FDO as these areobtained (see FIG. 20E). The correction coefficients PC, RC, and BC areselected based on the selection pulses PDO, RDO, and FDO, and hence theselection output comp becomes the calculated value as shown in FIG. 20F.Upon multiplying the selection output comp and the monochrome picturesignals (FIG. 20A), the respective monochrome picture signals SR′ (=Ro),SG′ (=Go), and SB′ (=Bo) become these as shown in FIGS. 20G, 20H, and20I. Considering the picture pattern Pa portion (time point t0):

SR′=0.5*1.5=0.75

SG′=1.0* 1.5=1.5

SB′=1.0*1.5=1.5

[0138] Herein, considering the R, G, and B mixing ratio at the timing t0when the picture pattern Pa is obtained, the result is:

SR′:SG′:SB′=0.75:1.5:1.5=1:2:2

[0139] The R, G, and B mixing ratio at the time of input is:

SR:SG:SB=0.5:1.0:1.0=1:2:2

[0140] Thus, the mixing ratio shows almost no change, and is heldconstant. In other words, even if the foregoing processing is performed,the color saturation shows no change.

[0141]FIG. 21 is a system diagram showing another embodiment of themonochrome judgment circuit 90R of R out of the monochrome judgmentcircuits 90R, 90G, and 90B. Also with this configuration, the circuithas a pair of delay circuits 110 and 112 using flip-flop circuits andthe like.

[0142] The input and output signals SRa and SRb (FIGS. 22A and 22B) ofthe one delay circuit 10 are supplied to a first adder 130, and addedwith the polarities shown, thereby to obtain a difference signal SRDatherebetween (FIG. 22D). Similarly, the input and output signals SRb andSRc (FIGS. 22B and 22C) of the other delay circuit 112 are supplied to asecond adder 132, and added with the polarities shown, thereby to obtaina difference signal SRDb therebetween (FIG. 22E).

[0143] The first difference signal SRDa is supplied to a firstcomparator 134, and subjected to level comparison with a level L1corresponding to the difference between high level and low level. Whenits level is higher than the reference level HL, a high-level comparisonoutput SRCa is obtained (FIG. 22F).

[0144] Similarly, the second difference signal SRDb is supplied to asecond comparator 136, and subjected to level comparison based on alevel L2 corresponding to the difference between low level and highlevel. When its level is lower than the reference level LL, a high-levelcomparison output SRCb is obtained (FIG. 22G).

[0145] Then, the comparison output SRCa from the first comparator 134 issupplied to first and second AND circuits 142 and 144, and thecomparison output inverted at an inverter 148 is supplied to a third ANDcircuit 146. Further, the comparison output SRCb obtained from thesecond comparator 136 is supplied to the first and third AND circuits142 and 146, and the comparison output inverted at an inverter 150 issupplied to the second AND circuit 144.

[0146] As a result, the detection pulse PDR corresponding to the picturepattern Pa is obtained from the first AND circuit 142 (FIG. 22H), andthe detection pulse RDR corresponding to the leading edge portion of thepicture pattern Pb is obtained from the second AND circuit (FIG. 33I).Then, the detection pulse FDR corresponding to the trailing edge portionof the picture pattern Pb is obtained from the third AND circuit 146(FIG. 22J).

[0147] In this manner, it is also possible to detect a specific picturepattern by using the difference signal components of adjacent pixels. Inthis case, it is possible to reduce the number of circuit elements thanthose shown in FIG. 14.

[0148]FIG. 23 shows another embodiment of the image processing apparatus100.

[0149] This image processing apparatus 100 is of a digital type, so thata receiver 160 for digital interface becomes necessary in place of theA/D converter 64 of FIG. 10. The clock input from an input terminal canbe used as a clock for the receiver 160 and the D/A converter 70, andhence the PLL circuit 78 of FIG. 10 becomes unnecessary. The otherconfiguration is the same as in FIG. 10, and hence the descriptionthereon is omitted.

[0150] Any of the values of the horizontal and vertical frequencies, thevalues of the correction coefficients PC, RC, and FC shown in FIG. 11,the value of the number of pixels n involved in the correctionprocessing, and the like is one example. For example, when peak and edgepatterns are detected by using 2n+1=5 pixels wherein n=2 where n is thenumber of pixels, it is possible to respectively detect the peak patternmade up of a pixel whose number is 1, the peak pattern made up of pixelswhose number is 2, and both edges of the peak pattern made up of pixelswhose number is not less than 3. Therefore, the suitable correctionaccording to each of the patterns becomes possible. It is also possibleto set different correction coefficients for respective patterns, whichcan be implemented by preparing a large number of correction values inthat case.

[0151] Further, the foregoing correction values and the like are to beappropriately selected according to the characteristics of the monitorto be used and the characteristics of the signal transmission system.

INDUSTRIAL APPLICABILITY

[0152] An image processing apparatus in accordance with this inventionis available for a picture display apparatus such as a computer displayrequired to have high fidelity and high resolution.

1. An image processing apparatus comprising pixel judgment means andpixel correction means, each receiving digital input picture signals ofR, G, and B, respectively, wherein said pixel judgment means includestarget pixel detection means for detecting a target pixel having a peaklevel out of said input picture signal, and edge detection means fordetecting an edge from a total of 2n+1 pixels of the target pixel and npixels preceding and succeeding the target pixel; wherein said pixelcorrection means includes correction coefficient selection means forselecting a peak level correction coefficient according to an outputfrom said target pixel detection means, and for selecting an edgecorrection coefficient according to an output from said edge detectionmeans; and wherein a level of the target pixel is corrected and an edgeof said input picture signal is corrected with a pixel of said inputpicture signal being corrected according to said peak level correctioncoefficient and said edge correction coefficient, respectively.
 2. Theimage processing apparatus according to claim 1, wherein said pixeljudgment means comprises a plurality of monochrome judgment circuits andOR circuits.
 3. The image processing apparatus according to claim 2,wherein said monochrome judgment circuit comprises a pair of delaymeans, a level judgment unit for judging levels of the target pixel andthe pixels preceding and succeeding the target pixel, and an edgejudgment unit for judging the leading and trailing of said target pixelwhen n=1.
 4. The image processing apparatus according to claim 3,wherein each of said level judgment unit and edge judgment unit includesa level comparator.
 5. The image processing apparatus according to claim1, wherein according to said detection result from the pixel judgmentmeans, the correction coefficient to be added to the detection result isto be switched.
 6. The image processing apparatus according to claim 1,wherein R, G, and B of the target pixel are respectively multiplied bythe same correction coefficient to prevent the color balance from beinglost upon correction of the peak level and the edge of said targetpixel.